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lenord
04-12-2006, 01:44 AM
Anyone,

I had to take some pieces in to a local shop to get them welded. The results were kinda ify IMO. There were burn throughs and divots at nearly every weld. Some were near perfect though. I was wondering if y'all could give me an opinion here.
The pieces were 6 tombstone shaped 1/4" Al. plates, about 10" wide and 16" tall. What they did was to wrap 48" long pieces .040 Al sheet, 5" wide, around the edges. Then weld the two pieces together from inside. These make gear train covers for some scopes I am converting.
Is it that hard to weld .040 to .250 plate ? Should there be any burn through or divots at the welds ? They only tacked the sheet on in about a dozen places. I've seen some very good welding here and was wondering....Nice solid beads. I've watched a vid someone did a while back. The weldign looked great. I was expecting something close to this.

My usual method is to drill/tap about a dozen 4-40 holes in the edge of the plate to attach the sheet to the edge. This takes some time and I wanted to save some. By going back and fixing the welds, it will save some time, but not a lot.

Thanks
Lenord

torker
04-12-2006, 02:10 AM
Did they Tig or mig it?
Yes...that can be a tricky weld...especially from the inside.
Was the metal new and shiny clean? Does it look like they cleaned both pieces well before welding?
The easiest way to weld that is with a pulse equipped mig.
It'd tig ok also but you'd have to be on the ball so you didn't burn through the .040.
Biggest problem is you need a lot of heat to weld the .250 but very little to weld the .040. Add heat transfer into the mix and you could blow a hole very easily.

greywynd
04-12-2006, 02:37 AM
If you're familiar, compare that weld to steel, even there it would be somewhat tricky because of the thickness differences. However, with teh aluminum, I could see big help would be to use a hotplate and preheat the thicker plate. Once it's preheated, and the strip placed around (it will absorb heat from the plate unfortunately) it should make it easier. Personally, I would start an arc/puddle in from the edge of the .040 a ways, then work up to it. (Can always grind off the extra bead if necessary, especially when it's on the inside.)

Mark

winchman
04-12-2006, 02:42 AM
From my very limited experience, welding thin aluminum to thicker aluminum can be done, but it's pretty tricky. The thicker piece will really suck up the heat, and it will be really easy to burn through the thin piece while you're waiting for the puddle to form.

I'd be especially careful about cleaning the thin material, then I'd concentrate the heat on the thick part just off the joint. When the puddle formed, I'd work it toward the joint just enough to get the a small part of the thin piece into the puddle. I'd ease up on the heat input as I went. I'd continue down the joint, varying the heat input as I moved the torch back and forth from the thick to the thin material. I'd add the filler rod to the thin material, and let it flow down to the thick side of the joint.

For the parts you describe, it's going to be difficult to do it with the thick part horizontal, which is where I'd like it to be. The thin piece is going to want to expand and move away from the thick piece because of the curve, too. It's not an easy welding project.

Maybe someone with more experience will have a better approach and different opinion, but I think I'd stick with the screws.

Roger

winchman
04-12-2006, 02:09 PM
Well, I found some suitable material and tried it this morning. Amazingly enough, I didn't burn through completely, except at one end. However, there were several slightly bulged areas on the back side of the thin material.

I wasn't very successful at varying the heat input as I moved the torch, but just concentrating the torch mostly on the thick side with quick passes onto the thin side seemed to work reasonably well. I ended up with way too large a bead in most places, but about an inch of the six inches I tried actually looked decent.

Based on that, it's doable, but I'd need a LOT of practice before I'd do it on something important.

Roger

david_r
04-12-2006, 02:25 PM
Lenord,
I'd talk with the welders. They can tell you if it's just beyond what they are capable of doing. Ask them if it would be easier if you drill 3/16" holes in the sheet so they could plug weld it on.

torker
04-12-2006, 03:04 PM
There SHOULD be a "bump" on the .040 material if it is welded correctly. With something that thin you are going to have evidence of proper penetration on the backside of the weld.
As for plug welding .040 to .250 with 3/16" holes...good luck with that.
By the time you have the .250 hot enough...the hole in the .040 will be quite a bit bigger than you bargained for.

Alguy
04-12-2006, 04:05 PM
I agree with Torker you will need to see some evidence of penetration on alum. it will be a small or slight rise or bump in the metal. If you are just trying to learn the procedure, make some practice welds and then try to chisle the welds apart then you can see how well you are progressing. If you find the bump objectionable you can file it smooth and metal finish to your liking. I spent many years building steel and alum. truck cabs and bodies.
allen

Mike Burdick
04-12-2006, 04:25 PM
...My usual method is to drill/tap about a dozen 4-40 holes in the edge of the plate to attach the sheet to the edge. This takes some time and I wanted to save some. By going back and fixing the welds, it will save some time, but not a lot.

Lenord,

Another way of fastening your work is by using "drive screws". Just drill the correct size hole and drive them in with a hammer. No cleanup, they look good, hold tight, and don't cost very much. MSC has carried them in the past.

http://www.smithfast.com/images/udrive.jpg

http://www.smithfast.com/udrivescrew.html

lenord
04-12-2006, 04:41 PM
Thanks to all who replied and even tried it out in their shops ! I really appreciate the help.
There are a few welds where there is a bulge on the outside where they welded the thing. There are some that are divots. Some places have burn through that will require repairs. I'll recall this posting while I am repairing the parts. :mad:
Thanks for the link to the drive screws !! That is precisely what I will do next time I have to make these covers !

:D :D
Lenord

Evan
04-12-2006, 04:46 PM
My usual method is to drill/tap about a dozen 4-40 holes in the edge of the plate to attach the sheet to the edge. This takes some time and I wanted to save some.


Aluminum pop rivets (breakstem fasteners) with steel shanks work pretty well in blind holes. No tapping required. It's worth testing. The steel shank pop rivets have enough pull force to swell the inside of the hole slightly to make the rivet hold.

There are also blind side fasteners like pop rivets made specifically for blind holes that work very well but they are much harder to find in small quantities.

david_r
04-12-2006, 10:56 PM
torker,
Are you talking TIG? I don't think a MIG would have that problem.

wierdscience
04-12-2006, 11:31 PM
Just curious,what alloy did you use?

I've done a lot of MIG on aluminum and the alloy can make all the difference in the world.

Welding thin to thick is a chore,but possible,the wire size will have a bearing on that if they MIGed it.Smaller wire works better for me it that situation.

torker
04-13-2006, 12:38 AM
torker,
Are you talking TIG? I don't think a MIG would have that problem.
Ooops...yup, I'm a "tig head" so that's the first that came to mind. You're right...a mig (especially pulse) wouldn't have that problem.